1. Field of the Invention
The present invention relates to a solar cell module and a production process thereof.
2. Related Background Art
Solar cells which utilize solar energy are expected to be a clean and reproducible energy source, from residential use to large scale electricity generation.
In particular, the use of solar cell modules on roofs of buildings is predicted as a means of utilizing limited spaces. Solar cell modules built in roof structures hold great promise in reducing the construction cost of buildings because such solar cell modules are installed as part of the construction process and do not need frames for installation.
Durability against environmental conditions such as temperature, humidity, and mechanical shock are required when solar cells are used. For this purpose, solar cell modules used conventionally are made by sealing the solar cell elements in a filler and by covering the surface with a durable plastic film or glass plate.
A most preferable structure for integral type solar cell modules built into a building roof requires that the solar modules be made in the following manner: the front side surface is sealed by a durable plastic film protector; a reinforcing plate is used at the back side surface without using a frame; and the non-generating area is applied to plasticity processing integrally with the reinforcing plate.
A solar module of such structure, which is mechanically reinforced by folds formed therein, not by use of a frame, has the following advantages:
It has no joint between the main body of the cell elements and the frame, and has no need for water proof treatment; thus it is advantageous for water flow thereover. It also does not need material and operational steps for providing the frame, and results in a cost reduction of the installation. It is also lighter than the framed module, and is easy to handle.
Stiffness of the module can be advantageous for joining and overlapping at the construction step; consequently a strong and reliable construction can be made.
When a usual metallic material is used for the back reinforcing plate, it can be set on the building roof just like the usual roofing material. Consequently, reliability of the module as the roofing material can be increased; thereby, popularization of the module can be assured with the interchange ability of the module with the usual roofing material.
The present inventors have developed a solar cell module that includes a solar cell element, a back reinforcing plate, and a durable plastic film for environmental protection.
The protection of the back reinforcing plate by a durable plastic film is required to prevent peeling between the cell elements and the back reinforcing plate, and to protect from the leakage of water from rain.
There were observed the following problems in such a solar cell module, which is composed of solar cell elements and a back reinforcing metal plate and with integrally applied plastic processing.
At first, the filler within the module tends to be cracked at the folded portions, the filler being used to protect the cell elements and because the folding work creates large stresses in the folded portion peripheral of the filler material. This cracking causes problems not only to the appearance of the module but also deterioration of the cell elements due to the leakage of water through the cracked channel reaching to the cell elements. There is also the problem that the protection film tends to crack.
Usually a filler holder is embedded in the filler material of the solar cell module, and the peeling occurs between the filler material and the holder; the holder is torn because of the bending strain and the folded portion is subjected to whitening. This whitening also gives rise of problems not only in the appearance of the module but also deterioration of the elements caused by the flow of water. The filler holding material is embedded to protect the solar cell elements, it also prevents hot filler leakage during the laminating step of the solar cell modules under heat and vacuum, and it also guides the air to the outside of the module during the defoaming under heat and vacuum.
For these problems, the present inventors proposed, in JP-A 7-131048, a method in which the holder is removed from the folded portion. However, even this means is not satisfactory for producing solar cell modules commercially because of the following problems.
Elastic material that can absorb mechanical shock is used for the filler to protect the solar cell element. The filler tends to return to the original flat plate shape after the solar cell module is shaped by folding, since the filler cannot be folded because of the elasticity restoration, even after the back reinforcing plate is folded. There is a problem of so-called xe2x80x9cspring backxe2x80x9d, as a result of which the required folding cannot be obtained and an insufficiently sharp angle results. There is also a problem in which the peripheries of the module tend to deform wavelike. These problems occur when a low strength backing plate for reinforcement, for example a thin steel plate, is used.
Referring to FIG. 19, the peeling problem is explained. Peelings occur at the location shown by reference numeral 1905 when solar cell module 1901 is folded towards the side of back reinforcing plate 1902 and the force of elasticity restoration, which is the force of filler 1903 tending to return to the original shape before the folding, exceeds the adhesive strength between filler 1903 and back reinforcing plate 1902.
This peeling problem may occur during the folding, and it also may occur after a long period of outdoor exposure even though there was no problem immediately after the folding. In the case where peeling occurs only in a limited part, the space between the filler and the back reinforcing plate forms a channel for water flow and the electricity generation ability of the solar cell elements deteriorates.
There is also a problem that the presence of thick filler material causes difficulty in the folding of various and complicated bending shapes of the solar cell module.
The bending has problems also for workability.
When a so-called xe2x80x9cbenderxe2x80x9d, the most simple bending machine that bends material placed between a blade and a mold, is used, it is necessary to lift the blade up and down for every bending operation; it is time consuming and makes cost reduction difficult. This problem is more severe for solar cell modules that have many folded parts. When the module has an elongated dimension along the folding side, it is necessary to use a blade and a mold that are longer than the dimension, and the necessary large power makes the bending difficult.
There is also a problem when a molder usually called a xe2x80x9croll molderxe2x80x9d is used to fold the solar cell elements for the purpose of avoiding the problem associated with the use of the bender.
By referring to FIGS. 20-22, roll molders are explained.
The modules are molded step-by-step in several stages between the upper and lower molding rollers. Various shapes of the rollers are used for the roller molding.
FIG. 20 shows a schematic front view of upper and lower molding rollers.
The module material to be molded 2001 is placed between the upper roller 2002 and lower roller 2003, as shown in FIG. 20, and molded. The rollers have the function of transporting the module material 2001 at a constant speed in addition to the function of bending. The rollers also have the function of making necessary adjustments.
FIG. 21 is a schematic drawing of a group of the upper and lower rollers.
The module material is transported from the right side to the left side of the figure, and molded gradually. Complex and good molding is possible when the number of rollers is larger, since the molding step can be divided into many stages.
FIG. 22 explains the molding process in the roller molding.
The material is processed gradually in many steps as shown in FIG. 22 and molded to the final shape.
The merits of this molding method are that the complex cutting face of the mold can be made in one series of processing, it is possible to make a folding mold having the long shape of the solar cell module, and it is also possible to mold materials in good surface condition, with good shape and size precision.
However, there is a problem in this method in that cutting and concavities may be formed in the filler when the solar cell module is processed. There is also another problem that the process may cause scarring and cutting of the weather resistant plastic film.
These problems are explained by referring to FIG. 23.
FIG. 23 is a schematic front view of the upper and lower rollers and a solar cell module that is in the course of molding. As shown in the figure, the face of the solar cell module 2301 is pressed at the two points 2307, by upper molding roller 2305, when the solar cell module 2301 is folded towards the side of back reinforcing plate 2302. Since the filler is thick and has large elasticity in this part, problems of depression and tearing of the filler occur. Also, the problems of scarring and tearing of the wear resistant plastic film occur at the roller edges. In addition, it is a problem that molding size precision is impaired by the absorption of the molding load by the thick filler.
These are not only problems in the appearance of the finished module, but there also are the problems of cracking and peeling of the filler by concavities and cuts in the filler; the scars or damage to the filler may deteriorate the performance of the solar cell module by water penetration along the peeling and damage of the weather resistant film. It is necessary to increase the roller pressure in order to get sufficient folding effect of the rollers, because the pressure tends to be absorbed by the filler; and the high pressure also deteriorates the performance of the solar cell element.
As described above, the conventional method of shaping a solar cell module by folding is difficult and unreliable; thereby, deterioration of the solar cell modules has occurred in long term service.
An object of the present invention is to provide a solar cell module that is excellent in foldability and in durability.
The present invention is to solve the problems explained above and to attain the object mentioned above by a solar cell module comprising a weather resistant film, solar cell elements, a filler for encapsulating the solar cell elements, and a back reinforcing plate, characterized by the non-generating area having a flat plane area containing a thinner filler than the generating area, and that folding is applied to the flat plane area containing the thinner filler.
It is preferable that the filler thickness of the flat plane area containing the thinner filler mentioned above is not less than 5 xcexcm and not more than 1000 xcexcm.
It is further preferable that a material for holding the filler is buried in the filler and that the flat plane area containing the thinner filler does not have a buried material for holding the filler.
It is further preferable that the material for holding the filler is a non-woven fabric or a woven fabric.
It is further preferable that the non-woven fabric or woven fabric is a ceramic non-woven fabric or woven fabric, a glass non-woven fabric or woven fabric, or a polypropylene non-woven fabric or woven fabric.
It is further preferable that the weather resistant film is a non-oriented film.
It is further preferable that the back reinforcing plate is a metal plate.
It is further preferable that the solar cell elements are bendable.
It is further preferable that the solar cell elements are amorphous silicon solar cell elements having, on a conductive substrate, a metallic electrode layer, an amorphous silicon semiconductor layer, a transparent conductive layer, and a grid electrode.
It is further preferable that the solar cell elements are amorphous silicon solar cell elements connected in series with plural amorphous silicon solar cells that have, on a conductive substrate, a metallic electrode layer, an amorphous silicon semiconductor layer, a transparent conductive layer, and a grid electrode.
It is further preferable that the folding is made by using a roll molding machine.
The solar cell according to the present invention has durability against external environmental conditions such as temperature, humidity, wind, and rain since the weather resistant film protects the module.
Durability against external environmental conditions such as temperature, humidity, wind and rain is also afforded by the filler that encapsulates the solar cell elements, which also protects the solar cell from mechanical impacts.
Strength as a structure is maintained by the back reinforcing plate and by the folding. Thereby, a frame body is now unnecessary, which makes the module light and the cost reduced. Fixed installation is possible by using the folded part.
Since the fold shaping is applied at the flat area where the filler is thin, the amount of filler is reduced; thereby, bending strain is decreased and peeling between the back reinforcing plate and the filler is prevented. Also, the problem of spring back, in which the required bend angle is not obtainable and only an insufficiently sharp angle is attained, is overcome since the elasticity restoration of the filler is decreased. The problem of wave formation at the edge of a solar cell module when folded near the edge of the solar cell module is also avoided.
In addition, the problems of cutting and collapsing occurring in the weather resistant film and filler when folded by a roll molding machine are also avoided. The pressure applied to solar cell elements is reduced since the pressure on the presser roll of the roll molding machine is mitigated. Furthermore, the amount of filler to be used is decreased, which contributes to cost reduction.
The present inventors have studied the effect of the thickness of the filler by evaluating the folded part, in which evaluation test samples are prepared and allowed to bend.
At first, the filler thickness at the folded part was varied to 1 xcexcm, 5 xcexcm, 10 xcexcm, 100 xcexcm, 500 xcexcm, 1000 xcexcm, 1500 xcexcm, and 2000 xcexcm, for preparing test samples of the solar cell module.
The experimental samples were made as follows. Fillers in sheet form of 1000 xcexcm thickness were laminated on and under the solar cell elements. For the samples of filler thickness of 1 xcexcm, 5 xcexcm, 10 xcexcm and 100 xcexcm, the filler was coated onto the back reinforcing plate. For the samples of filler thickness of 500 xcexcm, 1000 xcexcm, 1500 xcexcm and 2000 xcexcm, filler in sheet form of 500 xcexcm thickness is laminated in required number of the sheet. In this way, the filler lamination of the folding area was made. These fillers and solar cell elements were inserted between a rectangular back reinforcing plate and a weather resistant film; a vacuum laminator was applied and the fillers were melted at 150xc2x0 C. Solar cell modules were thus prepared.
EVA (ethylene-vinyl acetate copolymer) was used as the filler.
The experimental samples, prepared in this way, were subjected to folding (bending) by a roll molding machine, and the appearance thereof was evaluated. The shape of folding was: the solar cell module was pulled down vertically by 1 cm along the lengthwise direction to the back reinforcing plate side. Table 1 shows the result.
Durability of these samples against the change of temperature was evaluated by visual observation of the folded part after 50 times repetition of a test cycle condition consisting of 40xc2x0 C. for 1 hour and 85xc2x0 C. for 1 hour.
Results obtained by folding using a mold and a knife are also shown in Table 1 for the purpose of comparison. The evaluation criteria are as follows. G (good): No appearance change was observed. P (poor) (1): Cut or concave. P (poor) (2): Peeling between the back reinforcing plate and the filler was observed.
In the sample of 1 xcexcm filler thickness, the adhesive strength of the filler lowered after the varying temperature cycles and peeling between the back reinforcing plate and the filler was observed. It has been found that sufficient adhesive strength requires 5 xcexcm or more film thickness. In the samples of 1500 xcexcm or more filler thickness, cutting of the weather resistant film and filler were observed in most portions along the folding line near but apart from the bent part by the roller molding machine. The folding by the bender also caused peeling between the back reinforcing plate and the filler since the adhesive strength between the back reinforcing plate and the filler was insufficient compared to the elasticity restoration of the filler and weather resistant film. It has been found that the filler thickness should be not more than 1000 xcexcm for the rolling work on the surface of the solar cell module without trouble and for preventing peeling of the filler.
As found, the problems mentioned before are surely solved by making the filler thickness, in the thinner flat area of the mentioned filler, not less than 5 xcexcm and not more than 1000 xcexcm.
In addition, by not burying the material for holding the filler, the solar cell element parts are protected by the filler holding material, flow out of the filler is prevented at an elevated temperature when the solar cell modules are laminated under vacuum and heat, the air remaining in the solar cell module is exhausted to the outside, and the problems causing deterioration of the solar cell module are avoided, including white turbidity of the folding part brought by peeling between the filler and the filler holding material and their cutting and the water flow therein.
Since the material for holding the filler is non-woven fabric or woven fabric, high light transmittance, high porosity, and high strength result. Flow out of the filler is further prevented at an elevated temperature when the solar cell modules are laminated under vacuum and heat, and the air remaining in the solar cell module is further exhausted to the outside. Decrease of the incident light is also kept at a minimum.
When the non-woven fabric or woven fabric is ceramic non-woven fabric or woven fabric, glass non-woven fabric or woven fabric, or polypropylene non-woven fabric or woven fabric, high light transmittance, high porosity, and high strength are provided. Thereby, sufficient protection against scratches and impacts to the solar cell module results. With the high light transmittance, the incident light decrease is at a minimum. Deterioration and discoloration for a long period of time are inhibited, and disadvantageous effects are prevented. Since the solar cell modules are not deteriorated when they are laminated under vacuum and heat, flow out of the filler is prevented at an elevated temperature in this process and the ability to exhaust the remaining air in the solar cell module outside is further enhanced.
Furthermore, when the weather resistant film is a non-oriented film, elongation of the weather resistant film is large, and the problem of breaking the weather resistant film in the step of folding is minimized. The non-oriented film also accommodates the variation of the filler from the thick parts to the thin parts, and cutting or wrinkling therefore does not occur even for a solar cell module in which the thickness varies significantly.
Furthermore, when the back reinforcing plate is a metal plate, necessary strength as a structure and excellent workability result. Excellent durability for outdoor use is secured thereby. Since metal plates have been conventionally used as roof materials, the convertibility therebetween is obtained. When the solar cell elements are bendable, the problem of cracking of the solar cell elements is avoided, and the thickness of the solar cell module can be made thin since limited rigidity is required, which contributes to making the weight small and the cost reduced.
When the solar cell elements are amorphous silicon solar cell elements having, on a conductive substrate, a metallic electrode layer, an amorphous silicon semiconductor layer, a transparent conductive layer, and a grid electrode, thin solar cell elements can be manufactured inexpensively; less thick solar cell modules contribute to reduction of the weight and cost.
When the solar cell elements are amorphous silicon solar cell elements connected in series with plural amorphous silicon solar cells that have, on a conductive substrate, a metallic electrode layer, an amorphous silicon semiconductor layer, a transparent conductive layer, and a grid electrode, manufacture of larger solar cell modules can be possible; thereby, an array of solar cells with a broad area can be constituted with a smaller number of solar cell modules. Required parts and workmanship per module are consequently reduced; thereby, the cost is reduced.
When the folding is applied by using a roll molding machine, fabrication is continuous with high productivity, and the folding is possible in a shorter period and less expensively than the case where a bending machine with a receiver mold and knife is used. Thereby, molding shapes with complicated cross-section is possible, and large and long modules can be manufactured simply.